Fiddling with Fonts

This week, waiting for PyQt5.4 to be released, I've been working on the Preferences dialog, and it's coming out rather interesting. Alongside here is a test version.

It's a stack of items. I built a whole little O-O heirarchy to make this. There's a parent class, ChoiceWidget, that displays a title line and on mouse-over, changes color and puts an explanation in the explainer box at the bottom. For the path-entry items, there's a PathChooser class that implements the path line-edit and a browse button, and when focus leaves the line-edit, checks that the given path is accessible according to some criterion (R_OK or X_OK) passed to its initializer, and if not, beeps and makes the line-edit pink. For the text-format items, there's a FormatChooser class that implements the color swatch and the sample highlight.

And then there's the font-chooser. Here I wanted to use QFontComboBox, which displays the available fonts using those fonts. Unfortunately it is rigidly designed. When told to display only monospaced fonts, it displays only the fonts the QFontDatabase thinks has that property.

Unfortunately, I am including two monospaced fonts with the program, Liberation Mono and another that I only just discovered, Cousine from the Chrome Core set. Cousine is basically the same as Liberation Mono except it has even more Unicode glyphs.

Either of these is a better choice than the next-best font, Courier New. The latter has about as wide a Unicode repertoire but it has a poor contrast between 1/l and 0/O. Alas, the QFontDatabase will not recognize either of the fonts that I am loading (using QFontDatabase.addApplicationFont()) as being actually monospaced. It will not return their names when asked for a list of monospaced fonts.

Which means that if QFontComboBox is set to display only monospaced fonts, it will not display the two that I most want the user to have access to. And although it claims to support the methods of its parent QComboBox, it ignores a call to addItem(string). So I can't add them. If I don't tell it to show only monospaced fonts, it of course shows every font available in the system, and takes quite a while to open first time.

I wasted quite a bit of time today trying to remedy this, first by trying to find some way to get QFontComboBox to show all but only the fonts I wanted it to show (the known monospaced fonts plus my two); then by trying to find a way to change my fonts so that QFontDatabase would recognize them as monospaced. That entailed a very lengthy search for a free or cheap TrueType font editor that would let me verify and set what I presume is a one-bit flag in the font file format that says "really, I'm monospaced." Didn't find one. Well, one, but it costs a bundle and its 30-day free trial version will not allow saving a modified font. So fuck them.

Actually, after all that, I'm not sure whether any amount of editing would help. The Mac OS Font-Book application does know these two are monospaced. It lists them when I make a "smart search" for monospaced fonts. So it may be that QFontDatabase is just prejudiced against added application fonts.

In the end I used a plain QComboBox loaded with the family names of monospaced fonts. I set it up so that when you make a selection from the list, the "explanation" box at the bottom changes to use that font.

I meant to finish the Preference dialog today, I really did. But the fiddling with fonts killed too much time. What's left is to implement the dialog widget itself, including the important "Set Defaults", "Apply", "Cancel" and "OK" buttons. A few hours more.